The invention is directed to a shielding container for the transportation and/or storage of spent fuel elements from nuclear reactors, said container having a cooling fin jacket made of several removable members fitted to the container.
Containers which are employed for the transportation and/or storage of spent fuel elements must safely seal in the radioactivity of the inserted material and demonstrate in strength tests that this is also guaranteed in extreme accident situations. However, they must simultaneously shield off the gamma and neutron rays set free in the radioactive decay reactions and lead off the heat of decay to the outside.
Known shielding containers mostly consist of a metallic base container having the required mechanical strength and the wall strength necessary for the shielding off of the gamma rays; customarily they are made of steel or a combination of lead and steel, and of an outer sheet of a neutron shielding material, mostly of small pellets of polyethylene cast in synthetic resin. There are normally welded or soldered to the metallic base article, heat conducting bars or fins penetrating the resin layer. They are necessary for enlarging the metallic surface in containers which are designed for a high neat conductivity and for carrying off the heat through the generally poor heat conducting neutron shielding layer.
It is a disadvantage of this construction that collisions of the container, which can even occur in routine operation, can lead to damage of the heat conductivity fins and resin layer and accordingly make necessary an expensive repair of the fin zone.
Furthermore a purification or, in case of contamination, a decontamination of the outer surface of the container formed by the fins or bars is difficult. Therefore this is protected by applying a protective shell in handling operations, in which there exists the danger of the contamination of the surface, thus for example, in the loading and emptying.
A further disadvantage of this known shielding container is that the number of heat conducting fins and the thickness of the neutron shielding must be designed for the maximum load predicted ynqvransportation situations. However, in a large part of the transportation and in using them as stored containers they contain spent fuel elements which are already so farly decayed in the fuel element storage basins of the nuclear power plant that in these cases both the neutron shielding as well as the fin surfaces of the container are over dimensioned.
Therefore it has already been proposed to provide the shielding container with a so-called cooling fin jacket constructed of several removable segments fitted to the container wall which are easily exchanged for repair and can be easily adapted to the particular transportation employed.
These cooling fin jackets, however, in many cases have the disadvantage that they are not intrinsically stable structures since they consist of a large number of individual segments. These can only be disassembled successively after removing the retaining members or again be reassembled with difficulty. This frequently results in time consuming and difficult handling. Furthermore in constructions which consist of many removable individual segments gaps between these are present which frequently either must be separately sealed with a permanently elastic, temperature resistant composition and continuously attended to or after a contamination if necessary can only be decontaminated through disassembling the entire individual elements.
As a result the filled container is without cooling elements for the duration of the decontamination and it can be heated up to an inadmissible extent.
Therefore it was the problem of the present invention to provide a shielding container for the transportation and/or for the storage of spent fuel elements from nuclear reactors which has a cooling fin jacket of several removable individual parts fitted to the container wall, which, however, avoids the above disadvantages, particularly is intrinsically stable, easily disassembled and reassembled and is free as possible from maintenance.